Polyethylene production with solid catalyst



Feb. 28, 1961 w. E. KENNEL ETAL 2,973,350

POLYETHYLENE PRODUCTION WITH soLIn cATALYsT Filed March 11, 1954 TS www@ United g Semis Para 2,913,350 POLYETHYLENE PRODUCTION WITH SOLID cArALYsr William E. Kennel, unster, Ind., and Edmundz Field and Charles A. Spiller, Jr., Chicago, Ill., and Gert H. Weisemann, Hobart, Ind., assignors to 'Standard il Company, Chicago, Ill., a corporation of Indiana :Filed Mar. 11, 1954, ser. No. 415,564 4 claims. (c1. 26o-94.9)

This invention relates to the production of polyethyleneI in aI commercial system employing solid catalyst of the molybdena-on-alumina type and a promoter such' as sodium. More specifically, the invention pertains to the solution of problems in carrying forward bench scale laboratory tests to commercial production. v l n It has been demonstrated in laboratory tests thatethylene in benzene solution can be polymerized Vinto normally solid polymers by solid catalysts such .as molybdena v ention is' to provide a commercial polyethylene plantV design for the production of about 25,000,000pounds' per year of solid polyethylene. A further object'is to provide improved methods and means'for the pretreatment of materials introduced into the reaction zone coupled with improved methods and meansfor effecting the reaction itself and for separating catalyst, ethylene, solvent rand by-product materials from polyethylene which is produced in the process. A particular object is to provide an improved method and means for transferring polymer from benzene solution to a water suspension. Another object is to provide the necessary safety factors required in commercial operations. A further object is to' provide a method and means for yields of high quality productslat minimum investment and operating costs and with maximum flexibility ofopl eration. Other objects will be apparent as the detailed description of the' invention proceeds. v

Briefly, the invention contemplates the' use 'of ethylene which is substantially free from oxygen, moisture and oxides of carbon but may contain'small amounts ofY other hydrocarbons such as propylene or ethane. The solvent is. preferablyV a purified nitration grade benzene which is dried to less than 20 parts per million of water. Preferably, makeup ben'zene has also been purified by preliminary contact with a catalyst-promoter mixture. The catalystvis preferably a partially reduced molybdena-onalumina which is4` introduced into the reactor as a slurry in bjenzeneat the Vrateof about .01 to .1 percent based onjin-troducedbeuzenelethylene solution. The preferred promotermis ,metallic` Asoliurnwhich is introduced into,

the reactor at the rate of, about 001 to .llweight percent based on incoming,benzenefethylene solution. Other catalysts1 of the molybdena-on-alumina type such as group Vnldmetal oxides on alumina, titania or zirconia may be used and other promoters such as calcium hydride, and certain other hydrides may be uused, instead of sodium, but` this does not mean that these other catalystsgor promoters are equivalents: of thoseherein described.

The reaetior'iiseffectedA in a stirred reactor operating afa press'rehigh Venougli to maintain liquid phase under conversion cr'l'ditio'ns's usually in therange of 500 to obtaining maximum' 20,000, e.g. 2,000 p.s.i.g., at a temperature in the range of 350 to 550 F., e.g. 465 F., at a weight space velocity yin the range of about 1 to 10, e.g. about 3 parts by weight of ethylene charged per hour per part by weight of catalyst in the reactor, with a quantity of catalyst in the reactor in the range of about 2 to 20, e.g. about 6 pounds per cubic foot. The ethylene is absorbed in benzene to give a 5 to 10, preferably about 7, weight percent solution which isemployed as fa feed stock. lIn the preferred examples, the time of contact and amount of catalyst in the reaction zone is controlled to give a reactor effluent containing approximately 2 weight percent of normally solid polyethylenethis is important from the standpoint of viscosity which, in turn, is important in controlling the -amount of catalyst which is withdrawn in the reactor efuent stream.

Suiiicient catalyst is separated, preferably by liquid centrifugal separators, and returned to the reactor so that the amount of catalyst therein remains substantially constant and the amount of catalyst in the final reactor effluent is substantially the same as the amount of fresh catalyst being introduced to the reactor. This nal reactor effluent stream is depressured to about to 500, preferably about 400 p.s`.i.g., and introduced intor an ethylene stripper, the bottom temperature of which should not exceed about 500 F., for removing about 99 percent of the unpolymerized ethylene and about 50 to 65 percent of the benzene solvent; the removed ethylene and solvent'may be recycled to the initial ethylene fabsorber to help supply incoming feed. n n

The solution leaving the base of the ethylene stripper should'contain at least about 4 to 6 or 5 percent polyethylene togetherwith the catalyst solids and thellatter are separated,- preferably by iiltratiomat a temperature in the range of 400 to 500 F. at this intermediate pressure. The catalystffree solution is then mixed with an amount of water which will supplyrthe heat of vaporization of the benzene .and which upon depressurizing will enable the transfer of the polyethylene from the benzene to give an aqueous slurry. yIt is important to add the water before depressuring, i.e. while the pressure in the'example is still about 400 p.s.i.a. The mixture of catalystfree solution and water is depressurized and introduced into a solvent stripper where the benzene `arid a portion' of the water is flashed overhead leaving a slurry of Water and polyethylene, said slurry beingjstripped` at atemperature'in the range of labout 140 to 190,e.g. 165 F.V to remove substantially all of the, benzene overheadand to leave less than 1 percent, preferably not more'than 0.1 percent, of benzene in the aqueous slurry of polyethylene which is then concentrated and dried in any manner well known to those skilled in the art..

The overhead from the solvent stripper is cooled in a particular manner to effect condensation of benzene and water and benzene is recovered from the uncondensed gases by adsorption on activated carbon, the unadsorbed ethylene being discharged to a surge drum and/or recycled in the system. TheA condensed water which is separated from benzene is returned to the solvent stripper and the benzene layervis passed to la dewatering. column for removing most of the Vremairung water contained therein, thence to a solvent stillfor removing lay-prodi ucts such as ethyl benzene or other alkyl benzenes and thence through a dryer for decreasing its water content preferably to not more than l0 parts per million.y

l, Provision is made for cooling reactors in case of shutdowns, reacting metallic sodium in the reactors with methanol or the like to make it non-hazardous a'nd'to by-pa'ssmaterial from reactors to a slop system for recovering valuable components. n

`rThe invention will be more` clearly understood from the following detailed description of a specific example of a commercial plant read in conjunction with the accompanying drawing which forms a part of this specication and which is a schematic ow diagram of said commercial plant. Y Referring to'the drawing, about 3,800 pounds per hour of ethylene from source is introduced by line 11 at a pressure of about 400 p.s.i.g. and a temperature of about 4 F. The ethylene should be at least about 99 percent pure and although it may contain small amounts ofv ethane or propylene, it should contain less than 50 parts per million of oxygen, a moisture content corresponding to a 50 F. dew point and should be substantially free from CO and CO2. The ethylene is vaporized by heat exchanger 12 and combined with` recycled ethylene, and the total'ethylene is introduced at the base ofabsorber 13 at approximately 65 F. Recycled ethylene is introduced into line 11 by line 14 at the rate of about 2,450 pounds per hour (containing about 5 to 6 percent benzene) at a temperature of about 150 F. About 156,160 pounds per hour of benzene containing aboutl 5,600 pounds per hour of ethylene is introduced by line 15 to the upper part of the absorber tower at a temperature of about 120 F. About 20 pounds per hour of ethylene and unabsorbed material is vented from the top of the absorber by line 16. Approximately 11,420 pounds per hour of ethylene dissolved in 156,160 pounds per hour of benzene is removed from the base of the absorber by liner 17, pumped by pump 18 to about 2,000 p.s.i.a., heated in exchanger 19 to a temperature of about 408 F. and thence distributed through heat exchangers 20 for close reactor temperature control to each of three reactors 21, each of which is 6 feet in diameter by v10 feet tali made of stainless or stainless clad steel and designed to withstand a reaction pressure greater than 2,000 p.s.i.a. Although only one reactoris shown in the drawing it will be understood that three of such reactors are employed in the plant.

The solid catalyst in this example is molybdena-onalumina containing 7.5 percent molybdena and is the type of catatlyst commonly employed in the hydroforrning of naphtha boiling range hydrocarbons. The particle size of the catalyst should be in the range of 10 to 100,k preferably 20 to 80 mesh. Such catalyst is charged into hopper 22 and thence fed at a controlled rate into a sealed rotary kiln 23 which discharges into jacketed cooler 24. Hydrogen from source 25 is preheated in exchanger 26 and then heated in heater 27 to about 1,000 F. and introduced into the discharge end of rotary kiln 23 which may be about 1 foot, 9 inches in diameter and 30 feet long and rotated at about 1 r.p.m., the kiln being operated under a pressure of about 2 p.s.i.g. Hydrogen and moisture from the inlet end of the rotary kiln is withdrawn by line 28 through exchanger 26 and circulated by pump 29 through condenser 30 to separator 31 from which water is Aremoved and hydrogen is recycled by line 32. The hot catalyst may be cooled in jacketed feeder 24 while in contact with a non-oxidizing gas such as hydrogen or ethylene which may be introduced by line 33 and thence transferred by line 34 topurge air from hopper 22 and to preheat the catalyst therein. The catalyst, on a dry basis, is thus charged to the system at the rate of about 45 pounds per hour andthe hot hydrogen is circulated in the reduction step at the rate of about 95 pounds per hour.

The cooled partially reduced catalyst is introduced into feed hopper 35 which periodically empties into feed hopper 36, the latter being pressured by ethylene from line 37, compressor 38 and line 37a to about 2,500 p,s.i.a. to facilitate transfer of the catalyst by screw conveyer 39 into slurry tank 40 in controlled amounts. Hydrogen may be employed as a pressuring gas instead of ethylene in order to prevent any possible pre-polymerization of ethylene. The slurrying medium may bea portion of the 7 percent ethylene solution in` benzene from line 17 and line 17a but it is preferably a benzene which contains 4 little or no ethylene, e.g. benzene from line 41. Benzene slurry of about 15 pounds per hour of catalyst in 270 pounds per hour of benzene is distributed into each of the three reactors by line 42.

The promoter in this example is metallic sodium which is introduced from source 43 into dowtherm jacketed Stor-- age tank 44 at a temperature of about 240 F. Molten.l sodium is alternately introduced into one of the blow' cases 45 and 45a and the blow case is then pressured with ethylene from line 37b to about 2,500 p.s.i.a. so that the liquid sodium may be metered by line 46 equally into each of the three reactors.

Eachof the three reactors is provided with a motor driven stirrer 47 driven at 250 rpm. and each reactor normally contains about 1,350 pounds of catalyst and 600 pounds of sodium. The reaction temperature is held at about 465 F. by controlling the temperature of incoming feed by exchanger 20 and the reactor pressure is maintained at about 2,000 p.s.i.a. At their upper endseac'h of the reactors Vis provided with downwardly sloping annular batlies 48 the purposeotwhichis tol p ovide an upper relatively quiescent settling zone'so that reactor eluent withdrawn through line 49 will contain a minimum amount of solid catalyst. The conditions here inabove described are designed to give a reactor etliuent'. containing about 2 weight percent of solid ethylene poly mer since such a solution is of proper viscosity for con-- trolling catalyst carry-over. Charge rates, temperatures,- ethylene concentration of the feed, etc. may be conf trolled within limits previously stated to provide a reactor eluent of the desired Viscosity. While it is not always essential that the reactor eiuent contain 2 weight percent of solid ethylene polymer, it should never exceed about 10 weight percent and usually should not exceed 5 weight percent, the important consideration .being the viscosity and avoidance of undue catalyst carry-over.`

The initial reactor effluent from each yreactor may contain about to 200, e.g.f150 pounds per hour of solid catalyst and in order to avoid depletion of catalyst in the reactor about 90 percent of this catalyst must be returned thereto. This is accomplished by liquid cyclones 50 and 50a which may be operated singly or in parallel to return a slurry containing about pounds per hour of catalyst by pump 51 to the lower part of the reactor. The iinal reactor eiuent, which contains about 15 pounds of catalyst from each reactor or a total of 45 pounds of catalyst per hour is withdrawn through line ,52 through pressure reducing valve 53 in which the pressure is reduced to about 400 p.s.i.a. At this lower pressure the stream is introduced into the flash zone of stripper 54 which is provided with-disc and doughnut baffles and which is heated at its base by withdrawing 96,500 gallons per hour of liquid through line 55 at about 470 F., pumping it to about 550 p.s.i.a. in pump 56, heating it to about 500 F. in heater 57 and reducing the pressure of the heated material in pressure reducing valve 58 in the return line. The material in the heat exchanger is at the indicated higher pressure to insure liquid phase heat exchange and prevent local overheating as polymer may degrade at temperatures above 500 F. The operation in vessel 54 effects a stripping of about 99 percent of the ethylene and about 50 to 65 percent of the benzene from the polymer solution, the overhead material being cooled in condenser 59 and separated in separator 60 ethylene (containing a small amount of benzene) may be returned by line 14 to absorber 13 and the benzene (containing about 3 or 4 percent of ethylene) may be returned by pump 61 and line 62 to the top of absorber 13.

The polymer solution leaving the bottom of ethylene stripper 54 through line 63 contains about 4 to 6, preferably about 5 percent polymer together with the solid catalyst which is next removed from this system by lters 64, 64a and/or 64b; it should be understood that any known filters may be used (Sparkler lters being preferred) and that two may beoperated in parallel while one so that the 'is being cleaned. Torrione' remover of. en eata'tysttie iterea stream ffiey pees thingie eil-*afa "oaatrneri 6s before it passes througlv pressure r`reduei valve into the ash" ione of solvent stripper' 67whicl1" isoperatedat ssr of about 2y p.S`".i.g.` and: 165 F. teahl Confaluing about 171,100 pounds Holi!" f vvfe about 152 pounds per hour o 'f lj'hfie.Y from lilf 68 is Heated fo 200 F.` in exchanger 69 ehdiffo ed into theV eat'a1y"`fr'ee stream just ahead l"f pressur reducing valve y66 so' that on re'c'luetionl of p vl"'e theivsolid poly'.- fr'ler may be"` transferred' from a' sol'tioi in benzenevv to a suspension' in water. Most of the benzene n l ethyl eisrremoved from the aoueofs ol the upper flash ione of stripper 67: n lith 70 and/gr. Steam .from line 7l iS iPtf if *bei Sbl'vfnf Stprerf rein the queens S'lufrylasY is feasible@ ,tltth theY stripper will have abenzene Scontent tantially hless 1 percent; This slurry is then inft'rodueedtonalong ventionalnwater separation and drying system 72wfrom which the final product polymer is: removed by `cc'knnveyer line 73 and wat'erandresidual benzene are' returned by line 74'Aand line 68 to'the stream entering pressure reducin'gjyalve' 66.V e Y The overhead from stripper 67A passes through cooler 75' to'con'densate separator 76 from which `the condensate is introduced into decanter 77. Gasesvfrom separator 76 pass through refrigerated condenser 78 lto separator 79 which operates at about 45 P. ana' lvcondensate from 79L islint'ro'duced by line 80 to' decanter 77. Ucondensed gas. fron separator 79 ispass'edv by blower til and line 82 it'o" one of the; benzene adsorption towers 83 and ssa which are packed with' activated carbon; usev of refrigerated condenser-cooler 78 permits operation` of adsorpti 1ers without internal cooling area'i to remove heat o'rption'. The on-s'trea'm adsorber iSoper'ated at abo'lt` 140" F. to adsorb benzene from ethylenewhich is then passed by blower 84 through line 85Y to line`70 andYor to ethylene surge tank 86. The adsorber tower which is`n'ot onls'tream may be regeneratedby steam introduced through line 87 to remove benzene through line 8*.8, this stream being cooledin cooler 89 anddischarged intoY decianter 90 from which water condensate may be withdrawn. Decanted benzene from decanter 90 and decant'erf'l'? is introduced linto solvent surge tank 91from which this" benzene is passed by pump 9.2 andheater 93 to" devvateringcolumnlif which may operate ata bottom temperature of '178 F. and under a pressnreof .5;p.s.i.g. The overhead from this'ltower is condensed in` condenser 9S, water` is withdrawnvfrom separator 96 and benzene is recycled as reflux byfpur'np 97.

Theidewa'tered solvent is then introduced by ,pump 98 to solvent still 99 which operates ata pressure of'.5 'p.'s.ig. with a'topltemperature of4 120 F. and a'bottomltemperature of 226 F. Alkyl benzenes such as ethyl benzene are removed from the system by line 100. The benzene is condensed in cooler 101 and that portion which is not required for reux is introduced from receiver 102 by pump 103 through line 104 to one of the drying towers 105 and 106 which contains a suitable desiccant such, for example, as 1,500 pounds of Florite. It should be understood, however, that any other drying systeml may be employed which will remove the moisture content to below about parts per million. The dried solvent is introduced into benzene accumulator tank 107 from which it is passed by pump 108 and heat exchanger 109 to line and the upper part of absorber 13. At least a part of the benzene from this source may be introduced directly through line 110 directly -to line 17 instead of to the absorber` and this source of benzene is preferred for the catalyst slurrying step because it contains substantially no ethylene.

Make-up solvent is introduced to the system from source 111 and purilication system 112. Nitration grade 6 beniene isY pieferlly employed Abut in order to obtain the'v neces`y hgldegfree of purity' and to' remove pos sible'catlyst contaminants, such beiz'ene'is` not only dried to the deifdlw water eotent but. is' preferably also contacted with catalyst and promoter in a' solvent purifyingtower' whicr forms a part' o'fpurvifieatoi system 112. Thiis for purifying 1'80` pounds'per honi' of make-up benzene a" solvent `pn'rnfer may be a 6 fo'o't tower 2 feet in dineter provided with an agit''to an'd containing 170 pannes* of oroly'ttefige-omlnmina catalyst' ma 34 periode o'f sodium" o'iQsodiumjhydiide, .the purification being effected1 at apr'ss'ure of about' ,3h90 p.s`.i.'=a`. at. temperatueof 350 to 400 F It"l isl necessary,A of course, to'lter thencatalyst from' the purified solvent before the purified olv t le' introduced byline 1313' t" 'o'lvent'st'illQ oregolng ,lefs'r'ption'A 's` 1c" 'le to normal' opi n i nq'oifthe` plant;` Drig pe s" of plant startup, oil-grade polyfn rnaybei Lproi'd'ueed for short' periods; irl this c'sei thes "processing steps are followed down"- st'en from vther reforas'lnfor normal operationv except niet the Isoir/nier" segregated. To take care' of shutdow'ns' and to take care of the startupl of onefre'act'or while others are' oil-stream" without contaminating product polymea' slcall'ed ,slop,psystein" is provided. The design of such' system", is on the bas'is tht only one re'- acto will beVv shut downv at any one'tiin"'e'.',` f

The -flrst step in shut-down procdure after stopping ethylene flow to the reactor is to ush out residual polyusing vbenzene from accumulator tank 107. 'Ihe flushing is carried out` at' about 400 F.' and 400 p.s.i'.a. it'm'ay require about 1.5 hours.` The: lienze'ne-poly?l mei; solution its'v passed by' line 114- through cooler 115 'andba'ck pressure control valve' 116toY slop llash tower 1'17.` flhe pressure" in' thev reactor is` theri reduced to'- 1y t'rnopher'eby'vventing through'afre'ux oondenser system 1'1'81 and returningI condensed benzene to the reactor; in this'vvay'xtemperature is reduced to the atmospheric boiling point of benzene. Al small portionv of the benzene-is then withdrawn from the reactor into a settling tank 119 to make room for the addition of methanol. .The methanol is added from tank 120 in' the amount necess'ry t react' with all of the sodium. The hydrogen evolved is vented through' rthe reflux condenser system' 118;" The amount of methanol required,- about" 1,000 pounds',l is added' over a two hour period, thel heatv of reaction" beingA removed" by vaporizatlon and reflux of the benzene. After disposal ofthe sodiuin',y the' rejaeto'r contents' a're" pumped into' settling tank 119'; stream of water ismixed'with the benzene'V by line 12`1Yto`ex'tract the sodium` lcoholatel After da" period"V of' settling'jin tank 119 lthe aqueous layer", dumped andthe benee is" returned to make-up'l storage. n n n i Asa'bove stated, slop reactor e'iueint,` which may r= s 'ullt when` a reactor is coming onstrea'm or when, for some reason,y it vis producing dif-specification: polymer, is introduced into flash tower 117 which functions in a manner similar to ethylene stripper 54, the overhead being passed through cooler 122 to separator 123 from which ethylene is recycled by line 124 and compressor 12412 to the base of absorber 13 and benzene is returned by line 125 and pump 125a to separator 60. Heated water at about F. from line 126 is added to the polymer-benzene solution leaving the base of tower 117 through line 127, the mixture is passed through pressure reducing valve 128 and the mixture is ashed into slop solvent stripper 129 which operates at about 2 p.s.i.g. and from which the aqueous slurry of olf-grade polymer is withdrawn as waste through line 130. Overhead from the slop solvent stripper is cooled to about 110 F. in exchanger 131 and introducted into separator 132. Overhead from this separator is passed by compressor 133 through refrigerated cooler 134 wherein it is cooled to a temperature of about 45 F. before being introduced into separator 135. Thus only a re1- atively small amount of ethylene and benzene will be vented from the top of separator 135 and most of the solvent will be introduced by lines 136 and 137, respectively, to decanter 138 from which water may be removed through line `139 and solvent by line 140 to makeup solvent storage.

From the foregoing description it will be apparent that the objects of our invention have been attained. The commercial plant hereinabove described is designed to produce polymer at therrate of about .83 pound per pound of catalyst per ,hour with a catalyst life of about 90 hours corresponding to vabout 75 pounds of polymer per pound of catalyst. The residence time in reactors when calculated on -a 100 percent benzene basis is about one-fourth hour. f r a For over-al1 economyfin operation it is important that solvent losses be reduced toa minimum. From the foregoing description it will. be seen that this is accomplished by a combination of features including vthe use of refrigerated condensers 78 and 134, ,the use `of, activated carbon adsorption towers 4$3, the recycle: of solvent-containing water through lines 68, 74 and other parts of 'the system and the use of the described sloprecovery system.

While` a specic example of the invention has been described in great detail, it should be understood that the invention is not limitedrthereto since alternative operations and operating conditions will be obvious from'the foregoing description to Vthose skilled in the art.

` l. In a process for polymerizing ethylene to a normally solid polymer from a solutionA ofy ethylene in benzene by means of a solid metal oxide polymerization catalyst and a promoter, the method of operation which comprises stripping 1 about 99 percent` of the ethylene and about one-thirdto two-thirds of the benzene from the reactor eluent at apressure in the range of about t100 to 500 p.s.i.g. which is sufliciently high to permit recycle of benzene to an kabsorption step without necessity of compression, ltering residual solids from the remaining concentrated benzene solution which contains residual dissolved ethylene, adding sucient hot water tothe concentrated benzene solution while it is at a pressure in the range of 100 to 500 p.s.i.g. to supply heat of vaporization of the Ybenzene and to provide a carrier fork solid polyethylene, depressuring the mixture to rsubstantially atmospheric pressure and stripping theliquid slurry resulting from the depressuring step,cooling the overhead from the stripping operation to a temperature obtainable by condenserwater, separating uncondensed vapors from condensate thus produced and cooling the uncondensed vapors to a low temperature by a refrigerated condenser, and adsorbing benzene from uncondensed vapors separated Vfrom condensate produced by the refrigerated condenser whereby the low temperature produced by low temperature of the last named uncondensed vapors Ymaintains the adsorbing agent at a suflciently low temperature to provide retention of benzene without the necessity of abstraoting heat from the `adsorbent by indirect heat exchange. K l

2. The method of claimvl which includes the -further steps of recovering'benzene from adsorbent by blowing steam therethrough, condensing said steam together with said .steam in recoveredzsolvent, combining the resulting condensate with condensate produced lby the condenser and refrigerated condenser respectively, removing from the condensate water whichseparates therefrom as a separate phase, dewateringY the solvent from which the water phase has been separated to obtain a solvent containingrnot more than 20 parts per million of water and separating from the solventcomponents which are higher boiling than benzene.

3. In a process for polymerizing ethylene to a normally solid polymer from a solution'of ethylene in .benzene by means of a solid metal oxide polymerization catalystand a promoter, the method of operationy which comprises introducing molybdena-on-,lalurnina catalyst from'a feeding zone into a reductionzone, passing hydrogen through said reduction zone atta temperature in the range of 800 to 1100"y F., recycling hydrogen from the reduction zone through a cooling zone and Water separation zone and heat-ing zone back to said reduction zone, cooling the reduced catalyst with -a non-oxidizing gas and introducing at least a part of said gas after the cooling step into said feeding zone for preheating the catalyst in the feeding zone and displacing air therefrom, pressuring the cooled catalyst with a non-oxidizing gas to a pressure higher than the pressure of the'polymerization zone,

slurrying the pressured catalyst in benzene and introducing catalyst -into the reaction zone as a slurry in said benzene. i 'l v 4. In a process for polymerizing ethylene to a normally solid polymer from 4a solution of ethylene in benzene by means of a solid metal oxide polymerization catalyst and a promoter, the method of operation which comprises leffecting a reactor shut-down by displacing reactor c ontents with benzene, cooling the benzene in the reactor by reux cooling during depressuring of said reactor, withdrawing a part of said benzene from the reactor to provide space for suiiicient alcohol to react with sodium promoter in the reactor, introducing alcohol into the rei actor to convert the sodium into sodium alcoholate and liberate hydrogen, venting hydrogen from the reactor without loss of benzene by reux condensation and separating benzene from sodium alcoholate.

' VReferences Cited in the ile of this patent i :wirv

UNITED STATES PATENTS 2,400,129 Nelson May 14, i946 2,634,260 Carnahan Apnfl, s 2,731,452

Field et a1. Jan. 17,1955 

1. IN A PROCESS FOR POLYMERIZING ETHYLENE TO A NORMALLY SOLID POLYMER FROM A SOLUTION OF ETHYLENE IN BENZENE BY MEANS OF A SOLID METAL OXIDE POLYMERIZATION CATALYST AND A PROMOTER, THE METHOD OF OPERATION WHICH COMPRISES STRIPPING ABOUT 99 PERCENT OF THE ETHYLENE AND ABOUT ONE-THIRD TO TWO-THIRDS OF THE BENZENE FROM THE REACTOR EFFLUENT AT A PRESSURE IN THE RANGE OF ABOUT 100 TO 500 P.S.I.G. WHICH IS SUFFICIENTLY HIGH TO PERMIT RECYCLE OF BENZENE TO AN ABSORPTION STEP WITHOUT NECESSITY OF COMPRESSION, FILTERING RESIDUAL SOLIDS FROM THE REMAINING CONCENTRATED BENZENE SOLUTION WHICH CONTAINS RESIDUAL DISSOLVED ETHYLENE, ADDING SUFFICIENT HOT WATER TO THE CONCENTRATED BENZENE SOLUTION WHILE IT IS AT A PRESSURE IN THE RANGE OF 100 TO 500 P.S.I.G. TO SUPPLY HEAT OF VAPORIZATION OF THE BENZENE AND TO PROVIDE A CARRIER FOR SOLID POLYETHYLENE, DEPRESSURING THE MIXTURE TO SUBSTANTIALLY ATMOSPHERIC PRESSURE AND STRIPPING THE LIQUID SLURRY RESULTING FROM THE DEPRESSURING STEP, COOLING THE OVERHEAD FROM THE STRIPPING OPERATION TO A TEMPERATURE OBTAINABLE BY CONDENSER WATER, SEPARATING UNCONDENSED VAPORS FROM CONDENSATE THUS PRODUCED AND COOLING THE UNCONDENSED VAPORS TO A LOW TEMPERATURE BY A REFRIGERATED CONDENSER, AND ADSORBING BENZENE FROM UNCONDENSED VAPORS SEPARATED FROM CONDENSATE PRODUCED BY THE REFRIGERATED CONDENSER WHEREBY THE LOW TEMPERATURE PRODUCED BY LOW TEMPERATURE OF THE LAST NAMED UNCONDENSED VAPORS MAINTAINS THE ADSORBING AGENT AT A SUFFICIENTLY LOW TEMPERATURE TO PROVIDE RETENTION OF BENZENE WITHOUT THE NECESSITY OF ABSTRACTING HEAT FROM THE ADSORBENT BY INDIRECT HEAT EXCHANGE. 